The present invention relates generally to semiconductor devices and, more particularly, to the formation of a dielectric film using a wet rapid thermal oxidation process.
Insulating materials, such as dielectrics, used in semiconductor devices are selected based on their electrical or other properties and their intended use. For example, a typical DRAM device can include a first area assigned to a memory cell array and a second area assigned to peripheral circuits. The memory cells in the cell array include a transistor coupled in series with a stacked-type or other storage capacitor. The transistor includes a gate dielectric layer such as an oxide. The storage capacitor, which stores charge to represent data, also includes a dielectric material disposed between two electrodes.
It often is desirable to select a dielectric material having a high dielectric constant for enhanced capacitance. For example, a tantalum oxide (Ta2Ox) film formed by chemical vapor deposition (CVD) has a high dielectric constant (∈r) of about 25 to 30. Such a film can provide good step coverage and can be fabricated relatively easily compared to other insulating films having high dielectric constants. The tantalum oxide film typically is deposited as an oxygen-deficient oxide, and such oxygen deficient films typically are leaky. To improve the leakage current properties of the tantalum oxide film, an oxidizing treatment can be performed following deposition of the film.
Some oxidation processes are performed at elevated temperatures for an extended duration which can result, for example, in the diffusion of oxidizing species through the dielectric layer so that more oxygen is incorporated into the insulating film. This results in a better insulating film. Other defects, however, such as pinholes, can result in leakage current and, therefore, in an insulating film having a breakdown voltage that is not as high as desirable. Dielectric films with such defects do not have sufficiently high capacitance for the memory cells required for DRAMs of 256 megabits and larger. Thus, it is desirable to improve the techniques for enhancing the properties of tantalum oxide and other dielectric films used in DRAM and other semiconductor devices.